In recent years, there has been developed a signal output circuit which includes an operational amplifier capable of outputting output signal amplitude exceeding power supply voltage connected to the operational amplifier and output signal amplitude falling below ground voltage.
FIG. 1 is a block diagram illustrating a signal output circuit 100 which is an example of a conventional signal output circuit configured to output a signal exceeding power supply voltage. The signal output circuit 100 illustrated in FIG. 1 includes an operational amplifier 110 and a charge pump 120 configured to generate positive power supply for the operational amplifier 110 (see Patent Document 1 for example).
The signal output circuit 100 illustrated in FIG. 1 includes the charge pump 120 as a circuit generating a positive power supply voltage separate from the operational amplifier 110. The charge pump 120 uses power supply (121) voltage which are input voltage and ground (122) voltage to output positive voltage higher than output signal amplitude outputted by the operational amplifier 110, and outputs the positive voltage to the operational amplifier 110. The operational amplifier 110 outputs output signal amplitude exceeding the power supply voltage for the operational amplifier 110 by using the positive voltage outputted by the charge pump 120 as the positive power supply voltage for the operational amplifier 110.
FIG. 2 is a block diagram illustrating a signal output circuit 200 which is an example of a conventional signal output circuit configured to output a signal falling below the ground. The signal output circuit 200 described in FIG. 2 includes an operational amplifier 210 and a charge pump 220 configured to generate negative power supply for the operational amplifier 210.
The signal output circuit 200 illustrated in FIG. 2 includes the charge pump 220 as a circuit generating a negative power supply voltage separate from the operational amplifier 210. The charge pump 220 uses power supply (221) which are input voltage voltage and ground (222) voltage, which are input voltage, to output negative voltage lower than output signal amplitude outputted by the operational amplifier 210, and outputs the negative voltage to the operational amplifier 210. The operational amplifier 210 outputs output signal amplitude falling below the ground voltage by using the negative voltage outputted by the charge pump 220 as the negative power supply voltage for the operational amplifier 210.
As described above, the signal output circuit 100 can output the output signal amplitude exceeding the power supply voltage for the operational amplifier, and the signal output circuit 200 can output the output signal amplitude falling below the ground voltage.
In the conventional technique, the charge pump generates the positive power supply or negative power supply for use in the operational amplifier, which outputs the output signal amplitude exceeding the power supply voltage or the output signal amplitude falling below the ground voltage. The charge pump is a voltage generation circuit separate from the operational amplifier. The operational amplifier uses the output voltage of the charge pump as the positive power supply or negative power supply for the operational amplifier. As a result, the output signal amplitude exceeding the power supply voltage or the output signal amplitude falling below the ground voltage can be obtained. However, this configuration has a disadvantage in that the charge pump which is a circuit separate from the operational amplifier is additionally required and the circuit scale is large.
In view of this, an object of the present invention is to provide a signal output circuit, an operational amplifier, and a charge pump circuit which are capable of obtaining output signal amplitude exceeding power supply voltage or output signal amplitude falling below ground voltage without requiring a voltage generation circuit which is a circuit separate from the operational amplifier.